Halide Abstraction Competes with Oxidative Addition in the Reactions of Aryl Halides with [Ni(PMe(n)Ph((3−n)))(4)]

Density functional theory (DFT) calculations have been used to study the oxidative addition of aryl halides to complexes of the type [Ni(PMe(n)Ph((3−n)))(4)], revealing the crucial role of an open‐shell singlet transition state for halide abstraction. The formation of Ni(I) versus Ni(II) has been rationalised through the study of three different pathways: (i) halide abstraction by [Ni(PMe(n)Ph((3−n)))(3)], via an open‐shell singlet transition state; (ii) S(N)2‐type oxidative addition to [Ni(PMe(n)Ph((3−n)))(3)], followed by phosphine dissociation; and (iii) oxidative addition to [Ni(PMe(n)Ph((3−n)))(2)]. For the overall reaction between [Ni(PMe(3))(4)], PhCl, and PhI, a microkinetic model was used to show that our results are consistent with the experimentally observed ratios of Ni(I) and Ni(II) when the PEt(3) complex is used. Importantly, [Ni(PMe(n)Ph((3−n)))(2)] complexes often have little, if any, role in oxidative addition reactions because they are relatively high in energy. The behaviour of [Ni(PR(3))(4)] complexes in catalysis is therefore likely to differ considerably from those based on diphosphine ligands in which two coordinate Ni(0) complexes are the key species undergoing oxidative addition.